Unreal學(xué)習(xí)筆記2-繪制簡單三角形
1. 概述
之所以寫這個(gè)繪制簡單三角形的實(shí)例其實(shí)是想知道如何在Unreal中通過代碼繪制自定義Mesh，如果你會(huì)繪制一個(gè)三角形，那么自然就會(huì)繪制復(fù)雜的Mesh了。所以這是很多圖形工作者的第一課。
2. 詳論
2.1. 代碼實(shí)現(xiàn)
Actor是Unreal的基本顯示對象，有點(diǎn)類似于Unity中的GameObject或者OSG中的Node。因此，我們首先要實(shí)現(xiàn)一個(gè)繼承自AActor的類
頭文件CustomMeshActor.h：
#pragma once
// clang-format off
#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "CustomMeshActor.generated.h"
// clang-format on
UCLASS()
class UESTUDY_API ACustomMeshActor : public AActor {
GENERATED_BODY()
public:
// Sets default values for this actor's properties
ACustomMeshActor();
protected:
// Called when the game starts or when spawned
virtual void BeginPlay() override;
UStaticMesh* CreateMesh();
void CreateGeometry(FStaticMeshRenderData* RenderData);
void CreateMaterial(UStaticMesh* mesh);
public:
// Called every frame
virtual void Tick(float DeltaTime) override;
UPROPERTY(VisibleAnywhere, BlueprintReadOnly)
UStaticMeshComponent* staticMeshComponent;
};
實(shí)現(xiàn)CustomMeshActor.cpp：
#include "CustomMeshActor.h"
#include "Output.h"
// Sets default values
ACustomMeshActor::ACustomMeshActor() {
// Set this actor to call Tick() every frame. You can turn this off to
// improve performance if you don't need it.
PrimaryActorTick.bCanEverTick = true;
}
// Called when the game starts or when spawned
void ACustomMeshActor::BeginPlay() {
Super::BeginPlay();
staticMeshComponent = NewObject<UStaticMeshComponent>(this);
staticMeshComponent->SetMobility(EComponentMobility::Stationary);
SetRootComponent(staticMeshComponent);
staticMeshComponent->RegisterComponent();
UStaticMesh* mesh = CreateMesh();
if (mesh) {
staticMeshComponent->SetStaticMesh(mesh);
}
}
UStaticMesh* ACustomMeshActor::CreateMesh() {
UStaticMesh* mesh = NewObject<UStaticMesh>(staticMeshComponent);
mesh->NeverStream = true;
mesh->SetIsBuiltAtRuntime(true);
TUniquePtr<FStaticMeshRenderData> RenderData =
MakeUnique<FStaticMeshRenderData>();
CreateGeometry(RenderData.Get());
CreateMaterial(mesh);
mesh->SetRenderData(MoveTemp(RenderData));
mesh->InitResources();
mesh->CalculateExtendedBounds(); //設(shè)置包圍盒之后調(diào)用這個(gè)函數(shù)起效，否則會(huì)被視錐體剔除
return mesh;
}
void ACustomMeshActor::CreateMaterial(UStaticMesh* mesh) {
UMaterial* material1 = (UMaterial*)StaticLoadObject(
UMaterial::StaticClass(), nullptr,
TEXT("Material'/Game/Materials/RedColor.RedColor'"));
mesh->AddMaterial(material1);
UMaterial* material2 = (UMaterial*)StaticLoadObject(
UMaterial::StaticClass(), nullptr,
TEXT("Material'/Game/Materials/GreenColor.GreenColor'"));
mesh->AddMaterial(material2);
}
void ACustomMeshActor::CreateGeometry(FStaticMeshRenderData* RenderData) {
RenderData->AllocateLODResources(1);
FStaticMeshLODResources& LODResources = RenderData->LODResources[0];
int vertexNum = 4;
TArray<FVector> xyzList;
xyzList.Add(FVector(0, 0, 50));
xyzList.Add(FVector(100, 0, 50));
xyzList.Add(FVector(100, 100, 50));
xyzList.Add(FVector(0, 100, 50));
TArray<FVector2D> uvList;
uvList.Add(FVector2D(0, 1));
uvList.Add(FVector2D(0, 0));
uvList.Add(FVector2D(1, 0));
uvList.Add(FVector2D(1, 1));
// 設(shè)置頂點(diǎn)數(shù)據(jù)
TArray<FStaticMeshBuildVertex> StaticMeshBuildVertices;
StaticMeshBuildVertices.SetNum(vertexNum);
for (int m = 0; m < vertexNum; m++) {
StaticMeshBuildVertices[m].Position = xyzList[m];
StaticMeshBuildVertices[m].Color = FColor(255, 0, 0);
StaticMeshBuildVertices[m].UVs[0] = uvList[m];
StaticMeshBuildVertices[m].TangentX = FVector(0, 1, 0); //切線
StaticMeshBuildVertices[m].TangentY = FVector(1, 0, 0); //副切線
StaticMeshBuildVertices[m].TangentZ = FVector(0, 0, 1); //法向量
}
LODResources.bHasColorVertexData = false;
//頂點(diǎn)buffer
LODResources.VertexBuffers.PositionVertexBuffer.Init(StaticMeshBuildVertices);
//法線，切線，貼圖坐標(biāo)buffer
LODResources.VertexBuffers.StaticMeshVertexBuffer.Init(
StaticMeshBuildVertices, 1);
//設(shè)置索引數(shù)組
TArray<uint32> indices;
int numTriangles = 2;
int indiceNum = numTriangles * 3;
indices.SetNum(indiceNum);
indices[0] = 2;
indices[1] = 1;
indices[2] = 0;
indices[3] = 3;
indices[4] = 2;
indices[5] = 0;
LODResources.IndexBuffer.SetIndices(indices,
EIndexBufferStride::Type::AutoDetect);
LODResources.bHasDepthOnlyIndices = false;
LODResources.bHasReversedIndices = false;
LODResources.bHasReversedDepthOnlyIndices = false;
// LODResources.bHasAdjacencyInfo = false;
FStaticMeshLODResources::FStaticMeshSectionArray& Sections =
LODResources.Sections;
{
FStaticMeshSection& section = Sections.AddDefaulted_GetRef();
section.bEnableCollision = false;
section.MaterialIndex = 0;
section.NumTriangles = 1;
section.FirstIndex = 0;
section.MinVertexIndex = 0;
section.MaxVertexIndex = 2;
}
{
FStaticMeshSection& section = Sections.AddDefaulted_GetRef();
section.bEnableCollision = false;
section.MaterialIndex = 0;
section.NumTriangles = 1;
section.FirstIndex = 3;
section.MinVertexIndex = 3;
section.MaxVertexIndex = 5;
}
double boundArray[7] = {0, 0, 0, 200, 200, 200, 200};
//設(shè)置包圍盒
FBoxSphereBounds BoundingBoxAndSphere;
BoundingBoxAndSphere.Origin =
FVector(boundArray[0], boundArray[1], boundArray[2]);
BoundingBoxAndSphere.BoxExtent =
FVector(boundArray[3], boundArray[4], boundArray[5]);
BoundingBoxAndSphere.SphereRadius = boundArray[6];
RenderData->Bounds = BoundingBoxAndSphere;
}
// Called every frame
void ACustomMeshActor::Tick(float DeltaTime) { Super::Tick(DeltaTime); }
然后將這個(gè)類對象ACustomMeshActor拖放到場景中，顯示結(jié)果如下：
2.2. 解析：Component
-
Actor只是一個(gè)空殼，具體的功能是通過各種類型的Component實(shí)現(xiàn)的（這一點(diǎn)與Unity不謀而合），這里使用的是UStaticMeshComponent，這也是Unreal場景中用的最多的Mesh組件。
-
這里組件初始化是在BeginPlay()中創(chuàng)建的，如果在構(gòu)造函數(shù)中創(chuàng)建，那么就不能使用NewObject，而應(yīng)該使用如下方法：
// Sets default values ACustomMeshActor::ACustomMeshActor() { // Set this actor to call Tick() every frame. You can turn this off to // improve performance if you don't need it. PrimaryActorTick.bCanEverTick = true; staticMeshComponent = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("SceneRoot")); staticMeshComponent->SetMobility(EComponentMobility::Static); SetRootComponent(staticMeshComponent); UStaticMesh* mesh = CreateMesh(); if (mesh) { staticMeshComponent->SetStaticMesh(mesh); } } -
承接2，在BeginPlay()中創(chuàng)建和在構(gòu)造函數(shù)中創(chuàng)建的區(qū)別就在于前者是運(yùn)行時(shí)創(chuàng)建，而后者在程序運(yùn)行之前就創(chuàng)建了，可以在未運(yùn)行的編輯器狀態(tài)下看到靜態(tài)網(wǎng)格體和材質(zhì)。
-
承接2，在構(gòu)造函數(shù)中創(chuàng)建的UStaticMeshComponent移動(dòng)性被設(shè)置成Static了，這時(shí)運(yùn)行會(huì)提示“光照需要重建”，也就是靜態(tài)對象需要烘焙光照，在工具欄"構(gòu)建"->"僅構(gòu)建光照"烘培一下即可。這種方式運(yùn)行時(shí)渲染效率最高。
-
對比4，運(yùn)行時(shí)創(chuàng)建的UStaticMeshComponent移動(dòng)性可以設(shè)置成Stationary，表示這個(gè)靜態(tài)物體不移動(dòng)，啟用緩存光照法，并且緩存動(dòng)態(tài)陰影。
2.3. 解析：材質(zhì)
-
在UE編輯器分別創(chuàng)建了紅色和綠色簡單材質(zhì)，注意材質(zhì)是單面還是雙面的，C++代碼設(shè)置的要和材質(zhì)藍(lán)圖中設(shè)置的要保持一致。最開始我參考的就是參考文獻(xiàn)1中的代碼，代碼中設(shè)置成雙面，但是我自己的材質(zhì)藍(lán)圖中用的單面，程序啟動(dòng)直接崩潰了。
-
如果場景中材質(zhì)顯示不正確，比如每次瀏覽場景時(shí)的效果都不一樣，說明可能法向量沒有設(shè)置，我最開始就沒有注意這個(gè)問題以為是光照的問題。
-
單面材質(zhì)的話，正面是逆時(shí)針序還是順時(shí)針序？從這個(gè)案例來看應(yīng)該是逆時(shí)針。UE是個(gè)左手坐標(biāo)系，X軸向前，法向量是(0, 0, 1)，從法向量的一邊看過去，頂點(diǎn)順序是(100, 100, 50)->(100, 0, 50)->(0, 0, 50)，明顯是逆時(shí)針。
2.4. 解析：包圍盒
-
包圍盒參數(shù)最好要設(shè)置，UE似乎默認(rèn)實(shí)現(xiàn)了視景體裁剪，不在范圍內(nèi)的物體會(huì)不顯示。如果在某些視角場景對象突然不顯示了，可能包圍盒參數(shù)沒有設(shè)置正確，導(dǎo)致視景體裁剪錯(cuò)誤地篩選掉了當(dāng)前場景對象。
FBoxSphereBounds BoundingBoxAndSphere; //... RenderData->Bounds = BoundingBoxAndSphere; //... mesh->CalculateExtendedBounds(); //設(shè)置包圍盒之后調(diào)用這個(gè)函數(shù)起效，否則會(huì)被視錐體剔除 -
即使是一個(gè)平面，包圍盒的三個(gè)Size參數(shù)之一也不能為0，否則還是可能會(huì)在某些視角場景對象不顯示。
2.5. 解析：Section
Mesh內(nèi)部是可以進(jìn)行劃分的，劃分成多少個(gè)section就使用多少個(gè)材質(zhì)，比如這里劃分了兩個(gè)section，最后就使用了兩個(gè)材質(zhì)。如下代碼所示：
FStaticMeshLODResources::FStaticMeshSectionArray& Sections =
LODResources.Sections;
{
FStaticMeshSection& section = Sections.AddDefaulted_GetRef();
section.bEnableCollision = false;
section.MaterialIndex = 0;
section.NumTriangles = 1;
section.FirstIndex = 0;
section.MinVertexIndex = 0;
section.MaxVertexIndex = 2;
}
{
FStaticMeshSection& section = Sections.AddDefaulted_GetRef();
section.bEnableCollision = false;
section.MaterialIndex = 0;
section.NumTriangles = 1;
section.FirstIndex = 3;
section.MinVertexIndex = 3;
section.MaxVertexIndex = 5;
}
3. 其他
除了本文介紹的方法之外，也有其他的實(shí)現(xiàn)辦法，具體可以參考文獻(xiàn)3-5。實(shí)在是沒有時(shí)間進(jìn)行進(jìn)一步的研究了，因此記錄備份一下。另外，文獻(xiàn)6-7可能對了解UE關(guān)于Mesh的內(nèi)部實(shí)現(xiàn)有所幫助，筆者反正是看麻了。不得不說，這么一個(gè)微小的功能涉及到的內(nèi)容還真不少，看來有的研究了。
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